Which of the following nerves enters the orbicularis oculi muscle of the eye?

Appeared in: UP NHM CHO 7 Sept 2022(shift-1st)

Explanation

The orbicularis oculi is the muscle responsible for closing the eyelids, a key component of facial expression.
All muscles of facial expression are innervated by the Facial nerve, which is Cranial Nerve VII.
Therefore, the Facial nerve is the correct nerve that enters and controls the orbicularis oculi muscle.

Option A: The Abducens nerve (CN VI) innervates the lateral rectus muscle, which is responsible for moving the eyeball outward (abduction), not closing the eyelid.
Option C: The Trochlear nerve (CN IV) innervates the superior oblique muscle, which moves the eyeball downward and outward. It is not involved with eyelid closure.
Option D: The Oculomotor nerve (CN III) innervates most of the extraocular muscles that move the eyeball and, importantly, the levator palpebrae superioris which opens the eyelid. It does not control the muscle that closes the eyelid.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Innervation of facial and ocular muscles as background academic context rather than a clinical decision trigger.
Understanding this innervation is crucial for assessing facial nerve palsy (Bell's Palsy), where damage to the Facial nerve can lead to an inability to close the eye (lagophthalmos).
Nurses must protect the cornea from drying out (exposure keratitis) in patients with facial nerve palsy by applying lubricating eye drops, ointments, or taping the eye shut.
What if? If a patient presented with a drooping eyelid (ptosis) but could still close their eye forcefully, the issue would more likely be with the Oculomotor nerve (CN III), which controls the muscle that opens the eyelid (levator palpebrae superioris), rather than the Facial nerve.

How to Approach the Question

First, identify the muscle mentioned in the question: 'orbicularis oculi'.
Recall or determine the primary function of this muscle. The orbicularis oculi encircles the eye and is responsible for closing the eyelids (blinking, squinting).
Categorize this function. Closing the eyelid is an act of facial expression.
Recall the cranial nerve responsible for innervating the muscles of facial expression. This is the Facial nerve (CN VII).
Evaluate the other options to confirm your answer. The Oculomotor, Trochlear, and Abducens nerves primarily control the movement of the eyeball itself, not the muscles of facial expression around the eye.

Concept Tested & Keywords

QOLhFdBRE9Evl-fYyyE6Lv

E6 Anatomy Applied Ashalatha 4e pp. 426-428, 425-427

Practise the full UP NHM CHO 7 Sept 2022(shift-1st)

Attempt every question from this paper in a timed mock, then review the full solution for each one.